The primary sites of epithelial injury within the lung from ozone exposure are the trachea and central acinus. Initial exposure produces cellular injury and necrosis. Long-term exposure results in bronchiolar epithelial hypertrophy and hyperplasia and alveolar bronchiolization in the central acinus without epithelial injury or necrosis. In the trachea, the epithelium essentially resembles controls. While numerous biochemical studies have shown elevated levels of antioxidants in whole lung homogenates during the initial phases of exposures, the imprecision of the measurements has rendered interpretation of their biological significance, especially in terms of cellular resistant to injury, impossible. This project is designed to test two hypotheses: 1) the toxic effects resulting from an initial exposure to ozone on tracheobronchial epithelium are inversely related to the cellular level of antioxidant enzymes and glutathione and 2) the elevation in cellular levels of antioxidant enzymes is the mechanism by which tracheobronchial epithelium protects itself from ozone injury following repeated exposure. A multidisciplinary approach will combine biochemical assays to determine antioxidant enzyme activity and glutathione status of microdissected centriacinar and tracheal tissue with immunocytochemistry to define the cellular distribution of the antioxidant enzymes in the same regions following ozone exposure. These same parameters will a 1 so be determined in cultured cells isolated from exposed and unexposed animals and reexposed in vitro. The primary objective is to define the roles of antioxidants in the resistance of tracheobronchial epithelial cells to ozone toxicity.